This invention relates to a plastics material-packaged semiconductor device, and more particularly to improvements of a metal mounting unit on which an IC pellet is mounted.
A packaged semiconductor device 2 is already produced at present. This semiconductor device 2 as a whole has an outline shown, for example, in FIG. 1. The semiconductor device 2 is generally manufactured through the undermentioned steps. First, a flat metal plate is punched or etched to provide a metal frame assembly 4 indicated in FIG. 2. The metal frame assembly 4 comprises a large number of metal frame units 6 horizontally connected together by connecting bands 8, 10 to constitute a semiconductor device 2. For example, an IC pellet (not shown in FIG. 2) is mounted on the metal frame unit 6. This metal frame unit 6 further comprises an IC pellet-mounting part 12 which should be securely set in place and a plurality of lead strips 14 extending outward from the proximity of the periphery of the mounting part 12. One end of each lead strip 14 which lies near the mounting part 12 is left free. The lead strips 14 are all connected at the other end to a common connecting bar 10. The lead strips 14 are further connected together by a common connecting tie bar 16. A supporting bar 18 extends from the mounting part 12 to the connecting bands 8 and is connected to the connecting bands 8. Accordingly, the metal frame unit 6 is securely supported by the connecting bands 8, 10.
An IC pellet is mounted on the flat surface of the mounting part 12 of the metal frame unit 6. Numerous bonding pads on the IC pellet and lead strips 14 are electrically connected by bonding wires, respectively, using a bonding apparatus. In the molding steps, the IC pellet, mounting part 12 and the end portions of the lead strips 14 which lie close to the mounting part are encapsulated in plastics material. In the final step, the connecting band 10 and connecting tie bars 16 and supporting bars 18 are cut off to divide the metal frame assembly 4 into individual metal frame units 6. The lead strips 14 are bent as illustrated in FIG. 1, providing a semiconductor device 2 whose IC pellet is encapsulated in plastics material.
However, the semiconductor device manufactured by the above-mentioned process has been found to raise the undermentioned problem. Even where an IC pellet originally retained the property of a semiconductor element falling within the permissible range, a semiconductor device manufactured by setting the IC pellet on the mounting flat part 12 and encapsulating said IC pellet in plastics material somewhat lost its initial electric property, with the result that said property all fell outside of the prescribed range. This event appeared more noticeably particularly in an highly integrated circuit device than in a discrete semiconductor device.
The present inventors' study of the cause of the abovementioned drawback shows that contraction of molded plastics material directly imparts internal stress to the IC pellet; the mounting part 12 is distorted by said internal stress; and in consequence the IC pellet is subject to strains, giving rise to changes in its electric property.
Variation in the electric property of a semiconductor device whose IC pellet is encapsulated in plastic material admitting of mass production has posed a very serious problem. The reason is that the molding technique essentially adapted for quantity production of a semiconductor device actually indicates a prominent demerit due to a high percentage of manufactured semiconductor devices being disqualified.